Chemical investigations of marine organisms

The dissertation, entitled ‘Chemical Investigations of Marine Organisms,’ is composed of four research projects. The first three sections are focusing on the chemical studies of marine invertebrates. Projects included in these sections are: (1) antimitotic macrolides from the sponge Cacospongia mycofijiensis, (2) pyridoacridine alkaloids form the ascidian Cystodytes sp., and (3) imidazole alkaloids from the sponge Leucetta sp. cf. chagosensis . In the last section, the study of metabolites from a marine sediment-derived actinomycete is described.; In the chemical investigation of the sponge Cacospongia mycofijiensis , laulimalide and isolaulimalide were isolated, and it was found that both compounds exhibit paclitaxel-like microtubule-stabilizing activity with comparable potency to that of paclitaxel. The isolation, identification, and biological activity of both compounds are presented. The synthesis of the C-21–C-27 fragment of laulimalide was achieved in racemic fashion, utilizing a hetero Diel-Alder reaction as key step. The asymmetric approach toward the same fragment was attempted but led to mediocre yield with low enantiomeric induction.; The chemical study of the tunicate Cystodytes sp. led to the isolation of two new pyridoacridine alkaloids, arnoamines A and B. The alkaloids were the first pentacyclic pyridoacridines described that possess a pyrrole ring attached to the fg faces of the acridine moiety. The structure determination and cytotoxicity of both compounds are described, along with an unusual proton-deuterium exchange phenomenon.; A new 2-aminoimidazole alkaloid, (2E,9E)-pyronaamidine 9-(N-methylimine), was isolated from the sponge Leucetta sp. cf. chagosensis. Its structure was determined by means of NMR spectral analysis, and confirmed by X-ray crystallography.; Two new unusual $a,b$-unsaturated $g$-lactones were isolated from a marine sediment-derived actinomycete. The structure elucidation of both compounds was presented. Both lactones were found to be mildly toxic toward brine shrimp.